In the manufacture of semiconductor devices, photoresist masks are typically employed to protect areas which are not to be treated in a particular processing step, such as etching or implantation. After the processing step is completed, the photoresist is removed, and the next step in the manufacturing process is performed. For a given device, it may be necessary to apply and remove photoresist for as many as 50 or more different processing steps, and it is important that all of the photoresist be completely removed after each step to avoid contamination and defects.
Originally, photoresist was removed chemically, but this method is no longer in wide use due to environmental problems and the relative high cost. Today, photoresist is most commonly stripped or “ashed” in plasma reactors which employ an RF discharge to produce oxygen radicals which combine with the hydrocarbons of the photoresist to produce water and carbon dioxide which are in gaseous form and are easily disposed of.
As device technologies have shrunk to sub-nanometer designs, it has become increasingly difficult to achieve the required high resolution with the use of photoresist alone. To achieve the higher resolution needed for patterning sub-nanometer designs, semiconductor manufacturers have turned to using a thinner photoresist in conjunction with a hardmask material, such as silicon, silicon nitride or oxynitride or bilayers thereof, in conjunction with the photoresist or in place of the photoresist altogether. Typically, the photoresist is used to initially pattern the hardmask material, and it is then removed. The etch is then conducted through the hardmask layer versus the photoresist layer. This process allows for the use of thinner photoresist layers, and the hardmask provides more etch control during the etch process without the need to worry further with the presence of a photoresist layer.
Typically, a post ash clean is performed after each pattern formation and subsequent process, such as ion implantation and etching processes, to remove the residues remaining after the mask is ashed. Conventional post ash cleans are well known, and useful combinations include sulfuric/peroxide (SPM), ammonium hydroxide/peroxide (APM), or hydrochloric acid/peroxide (HPM), chemistries. When a hardmask is used in place of or in addition to photoresist, a hydrofluoric acid (HF) chemistry is also often added to the clean sequence. Unfortunately, however, when this hardmask etch is followed by a silicon etch, the above-mentioned conventional chemistries are not sufficient to remove all post etch residues associated with the hardmask.
Therefore what is needed in the art is a post clean process that avoids these disadvantages.